What is Instrumentation?

Seth PriceDepartment of Chemical Engineering

New Mexico TechRev. 1/8/15

Simple Instrumentation

http://3.bp.blogspot.com/-hVVw6rZDBn4/ToFRnKN2sxI/AAAAAAAAATU/1ZfrvzQeUEQ/s1600/thermometer.jpg

• Collecting data

• Manual measurements

• Slow sampling rates (1/10 Hz)

• Not controlling a process

Advanced Instrumentation

http://digital.natinst.com/public.nsf/$CXIV/ATTACH-AEEE-78KKB8/$FILE/Open%20Circuit.bmp

• Automated measurements

• Faster sampling rates

• Required for automated process control

Simple Control Loop

http://i-cdn.apartmenttherapy.com/uimages/re-nest/3-13-2008shower.jpg

Advanced Control Loop

http://upload.wikimedia.org/wikipedia/commons/thumb/c/c7/Change_with_Kd.png/320px-Change_with_Kd.png

http://www.aboutplcs.com/directlogic/images/dl205_app_pid.jpg

Back to the Shower Example….• Sampling Rate:

– How often measurements are taken

– Expressed as Hz

• Dynamic Range:– High measurement – low

measurement

• System Response:– How long it takes for a

change to take effect

http://epicthings.net/wp-content/uploads/2011/12/LED-temperature-shower-head.jpg

Back to the Shower Example…• Linearity:

– Does the response change correspond linearly to the control change?

(y = mx + b)

• Measurement Error:– Measurement does not

represent truth

• Disturbance/Impulse:– Unexpected step change

http://epicthings.net/wp-content/uploads/2011/12/LED-temperature-shower-head.jpg

The Magic of Automation

• Physical phenomena are converted to voltage or current through a transducer (input)

• Control voltages or currents are converted into physical phenomena

www.futurlec.com

Besides Voltage:

• Voltage In:– Temperature – Pressure– Humidity– Detection of light– Etc.

• Voltage Out:– Warning Lights– Motors– Voltage controlled

switches– Etc.

www.auberins.com http://www.globalspec.com

Control Loop

• Measurements + Logic = Control Loop– Compares current condition to set point– Adjusts to bring current condition to set point

• Ex: Cooling water for continuous reaction– Temperature must below TH

– Control a valve to increase cooling water flow rate

Iterative Improvements

• How can we make this process more accurate?

• How can we make this process more efficient?

• How can we make this process safer?

Increasing Accuracy

• Sample temperature in several places instead of just one, such that TAVG = T1 + T2 + T3

• Have a minimum temperature (TC) so that valve closes when T < TC

Increasing Efficiency

Increasing Safety

• Add leak detection: two flow meters, one on each side of the reactor, with flow rates F1 and F2.

– If F1 = F2, no leak.

– If F1 <> F2, leak is present, light warning LED.

– Operator checks warning LEDs periodically.

Keep Iterating and Expanding

http://www.snboiler.com/uploads/images/201209/18/CFB_boilers_(1).jpg

…Integrating the system

http://embeddedsystemnews.com/images/embedded/2009/08/common-wireless-sensor-networkarchitecture.jpg

…Fully Integrated Control System

http://www.jenriks.de/jenriks/wp-content/photos/jh1065_power_plant.jpg

…but it all starts here